Slight pixelation on 720p footage from after effects ?

[4mat]

I'm editing with fcp and all is well but when I export to after effects and back to fcp their is a very slight but noticable pixelation of the image causing jaggys to apear.
Anybody else noticed this ?
I've try'd using different output codecs from uncompressed 8bit 4:2:2 to the normal dvcprohd metods with no improvement's so I think it must be a resolution issue.
What am I missing ?
cheers
-matt

[4mat]

I've found that the only work around is to use a 1280x720 comp and drop the clip into that. Strange but true.